Bold fMRI of the visual cortex: Quantitative responses measured with a graded stimulus at 1.5 Tesla

Feroze B. Mohamed, Alexander B. Pinus, Scott H. Faro, Dhawal Patel, Joseph I. Tracy

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Purpose: To measure and quantitatively characterize an activity generated by the neurons of the visual cortex (VC) in response to graded luminous intensity contrast stimuli using a 1.5 Tesla scanner. Materials and Methods: Functional magnetic resonance imaging (fMRI) of the vc with the intrinsic blood oxygenation level dependent (BOLD) mechanism was performed by using a paradigm with a 5 × 5 flashing checkerboard pattern flickering eight times per second at eight luminance contrasts presented in a randomized order. The changes of the luminance contrast were obtained by varying the luminance intensity of the white checkerboard squares. Each of eight trials, corresponding to eight luminance contrasts, consisted of six "rest" and six "activation" epochs, repeated five times, amounting to 60 measurement periods per trial. During each epoch. 10 contiguous oblique axial-to-coronal slices covering the calcarine fissure region and parallel to a line through the anterior-posterior commissure (AC-PC) markers were acquired using a gradient-recalled echo planar imaging (GRE-EPI) sequence. Results: The measurements showed changes in the activation extent in the VC following the stimulus' rising luminance intensity contrast. In addition, the fMRI signal in those activated areas present throughout all eight trials, referred to as "common" voxels in this report, showed an increasing trend as a function of the rising luminance intensity contrast. Conclusion: These results suggest that the processes of the neuronal recruitment that affects the extent and number of activated neurons, and the neuronal enhancement that defines the magnitude of the neuronal activation are dependent on the luminance intensity contrast. These changes can be visualized and quantified using BOLD fMRI at 1.5 Tesla.

Original languageEnglish (US)
Pages (from-to)128-136
Number of pages9
JournalJournal of Magnetic Resonance Imaging
Issue number2
StatePublished - Aug 5 2002


  • BOLD
  • Visual cortex
  • fMRI

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging


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